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GPSMAP 188/188C Sounder Owner’s Manual 91
USING SONAR > UNDERSTANDING SONAR
Whiteline
When the sonar sound waves are reflected back by the bottom,
a hard bottom returns a stronger signal than a soft bottom. A
thin whiteline indicates a softer bottom, while a thick whiteline
indicates a harder bottom. Normally, a red line is used to show the
point where water meets the bottom. This line follows the bottom
contour, along with any significant objects lying on the bottom.
The unit uses the whiteline function to make the bottom layer
information easier to distinguish.
Whiteline OffWhiteline On
Thick
Whiteline: Hard
bottom
Thermoclines
A rough definition of a thermocline is a break in water where
the water temperature changes faster than the water above it.
Thermoclines are shown as the weakest colors.
One of the unique features offered by Garmin is See-Thru
®
technology, which allows the GPSMAP 188/188C Sounder to
hear both weak and strong signals simultaneously so as to identify
fish returns under the toughest conditions, such as suspended in
thermoclines or even hiding near structures. See-Thru technology
allows the transducer to see through thermoclines and locate fish.
Thermocline